Genetic structure and geneflow of Crowned Bullfrogs (Hoplobatrachus occipitalis) across ecological zones in Southwestern Nigeria

Abstract

<title>Abstract</title> Widespread amphibians are often assumed to be demographically resilient, yet increasing habitat modification and intensive harvesting may erode genetic connectivity. In Nigeria, edible frogs such as the crowned bullfrog ( <italic>Hoplobatrachus occipitalis</italic> ) are subject to intense and largely unregulated exploitation, despite limited information on population demography, genetic diversity, or population connectivity. Here, we combine mitochondrial and genomic data to evaluate patterns of genetic structure and gene flow in <italic>H. occipitalis</italic> across Southwestern Nigeria and within a broader African biogeographic framework. Mitochondrial haplotype analyses revealed a dominant, widely distributed haplotype shared across West, Central, and East Africa, consistent with a recent late-Quaternary expansion and weak phylogeographic structure. Analyses based on genome-wide nuclear SNP data showed weak but detectable habitat-associated structuring among savanna, rainforest, and mangrove populations. Nigerian populations exhibited moderate and relatively homogeneous nucleotide diversity (π = 0.0006–0.0015). Pairwise genetic differentiation was low overall, with the highest differentiation observed between Derived Savanna and Guinea Savanna populations (FST = 0.021). Effective migration surface analyses identified localized reductions in gene flow, particularly near urban and coastal centers, indicating that anthropogenic modification may constrain connectivity at fine spatial scales. These results demonstrate that <italic>H. occipitalis</italic> remains genetically cohesive at regional scales, yet locally vulnerable to habitat fragmentation, urbanization, and exploitation. These findings highlight the importance of maintaining breeding habitat connectivity and regulating harvest in rapidly developing landscapes to preserve genetic diversity in widespread amphibians.